One of the most versatile machines known to man is the pump. The number of applications to which such a machine can be put is limited, virtually, only by man's imagination. Pumps are used in virtually all significant machines engineered during the twentieth century. One particular application to which pumps are put is that of injecting one liquid into another. For example, dishwashing machines, particularly those of a commercial or institutional nature, typically require that a detergent or rinse additive be injected into the wash water contained in the washing chamber.
Various types of pumps have been used to accomplish this fluid injection application. Such pumps usually have a pump chamber in which a piston is slidably disposed for reciprocation. When the piston moves through its stroke in one direction, the fluid will be expelled from the pump chamber. Check valve arrangements can be utilized in order to insure that flow of fluid is in only one, and the proper, direction.
Frequently, such pumps utilize an external power source such as hydraulic or electric power in order to move the piston through the pump chamber. When such a power source is utilized, significant expenses can be involved because of both complications arising from design and cost of operation. Energy consumption by such pumps typically tends to be high.
The prior art has attempted to solve some of these problems by eliminating a high energy consuming structure. One of such prior art pumps not having all of the disadvantages as discussed above is illustrated in U.S. Pat. No. 3,547,560. That patent is assigned to the assignee of the present application. The pump of that patent enables one fluid to be injected into another without the necessary utilization of a separate external power source. Such a pump conserves power, is less complicated than externally powered pumps and requires no electrical hook up or other power connection. Additionally, it is less expensive to manufacture, purchase, and install.
The pump of U.S. Pat. No. 3,547,560 includes a pump body having an elongated chamber in which a dual acting piston is received. The piston has two opposed working faces with one of the faces having a diameter smaller than the other face. Additionally, the piston is normally biased by a spring to a first position wherein the piston is located relative to the pump body to form a first compartment adjacent one of the faces of the piston. A supply of the fluid to be injected is contained in this first compartment.
The pump body is connected adjacent the other face of the piston to a water conduit such as a supply line for a dishwashing machine into which the detergent or rinse additive is to be injected. A pressurized flow of water is directed through this conduit. As water starts flowing, some of the water will be directed by the conduit against the other face of the piston to force the piston upwardly against the bias of the spring. As the piston is forced upwardly, it dispenses the fluid contained in the first compartment through a metering device to a conduit which is itself connected to the pressurized water flow conduit. Such a configuration is designed to slowly meter fluid flow into the water conduit in order to effect a thorough mixing of the fluid with the water.
This type of pump has achieved a large measure of commercial success. It does, however, have disadvantages. It does not allow the amount of detergent or rinse additives being injected to be adjusted without varying the rate of inflow of washing water into the washing chamber.
The invention of the present application is an improved injection pump for injecting detergents and rinse additives as discussed above. It not only conserves power, is less complicated than many pumps presently in use for this application, and requires no electrical hookup or other power connection, but it also allows the rate of fluid injection to be varied independently of the flow of washing water into the machine's chamber.